Washington, DC: A police officer's use of a drug dog to sniff for the presence of illicit drugs during a lawful traffic stop is constitutionally permissible, even if there are no specific or articulable facts to suggest drug activity, according to a 6-2 ruling by the US Supreme Court on Monday.

The ruling reverses an Illinois Supreme Court decision that held that the use of a drug dog during a traffic stop without articulable suspicion of drug activity violates Fourth Amendment protections against unreasonable searches by the state.

The case before the court involved Roy Cabelles, who was pulled over on an Illinois highway for driving six miles above the posted speed limit. During the course of the traffic stop, a second police officer from the state's Drug Interdiction Team arrived and proceeded to walk a drug-sniffing dog around Cabelles' car. The drug dog alerted officers to the trunk of Cabelles' car. Police subsequently searched the trunk and found marijuana.

"A dog sniff conducted during a concededly lawful traffic stop that reveals no information other than the location of a substance that no individual has any right to possess does not violate the Fourth Amendment," Justice John Paul Stevens wrote for the majority. He added: "Official conduct that does not 'compromise any legitimate interest of privacy' is not a search to the Fourth Amendment. We have held that any interest in possessing contraband cannot be deemed 'legitimate,' and thus, governmental conduct that only reveals the possession of contraband 'comprises no legitimate privacy interest.'"

Had the drug sniff unreasonably prolonged Cabelles' traffic stop, Stevens opined that he would have likely held the conduct to have been unlawful.

Justice Souter wrote that the use of a drug dog constitutes a limited search because dogs are fallible and may routinely alert police officers to conduct searches of private property where no contraband is present. "The infallible drug dog ... is a creature of legal fiction," he wrote. "[I]n practice the government's use of a trained narcotics dog functions as a limited search to reveal undisclosed facts about private enclosures, to be used to justify a further and complete search of the enclosed area. ... Since the police had no indication of illegal activity beyond the speed of the car in this case, the sniff search should be held unreasonable under the Fourth Amendment and its fruits should be suppressed."

Justice Ginsburg opined that the use of a drug sniffing dog absent of any specific suspicions of drug trafficking is unconstitutional because it's unrelated to the circumstances which justified the initial police contact. "The sniff surely broadened the scope of the traffic-violation-related seizure," she wrote. "Today's decision ... clears the way for suspicionless, dog-accompanied drug sweeps of parked cars along sidewalks and in parking lots."